Ask Dr. SETI ®
Is it true that the background noise level seen by the antenna is approximately 290 Deg K ? For the purpose of determining the minimum detectable signal, I am using the following formula:
Psens (in dBm) = -174 dBm + 10 log B (in Hz) + Total Receive System Noise Figure (dB)
The above -174 dBm is 10 log K (Boltzmans Constant) less 10 Log (T), all converted to dBm
T being the temperature of the antenna in KelvinThis from Page 7.6 of the ARRL UHF/Microwave Experimenter's Manual.
Roy (via the ARGUS list)
The Doctor Responds:
The actual sky temperature varies, of course, with where you're pointing, with the minimum being 2.7 Kelvin (the cosmic background radiation), and the hot spots in the sky emitting some tens of Kelvin at microwave frequencies. The actual thermal temperature seen by your antenna will be higher, because sidelobes and over-illumination spillover mean that some Earth noise is in the pattern, and this adds to total noise. I figure a 50 Kelvin antenna temperature for my system when it's in birdbath mode, slightly more when it's pointed lower.
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this page last updated 6 August 2005
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